Solar cells
Solar cells are p-n junctions too, so they belong to the diode family. They are built so that light can fall on the junction.
Solar cell
When sunlight falls on a silicon p-n junction, a small electromotive force (potential difference) is generated across it. A junction used this way as a source of emf is a solar cell. One cell gives about 0.5 V; many cells in series and parallel give 12 V or 15 V and several amperes — a solar panel.
Figure to be added
Solar panels were first made to power satellites in place of batteries, when they were very expensive. Better manufacture and lower prices mean they now light homes and streets, and run watches, calculators and even solar cars.
Solar cells are seen as an answer to the coming energy crisis: they run on free sunlight, give out nothing that pollutes, and last a very long time — the first ones made still work.